Flyback transformer

ABSTRACT

Temperature increase becomes a problem with a flyback transformer of a television receiver since it handles a high voltage. In order to cope with this, it has conventionally been the usual practice to make the core gap sufficiently great to provide allowance for the design. With such a construction, however, the transformer becomes large in size, and the highvoltage stability thereof is deteriorated. In view of this, in accordance with the present invention, a temperature-sensitive ferrite is provided in the gap of the core to prevent the slope of the B-H curve from becoming unduly small and to stabilize the high voltage during normal operation. In case the temperature is increased, the Curie point of this temperature-sensitive ferrite is utilized to improve the temperature stability of the flyback transformer.

[ 1 May 9,1972

[54] FLYBACK TRANSFORMER [72] Inventors: Teruhiro Tsukuda,Moriguchi-shi; Takashi Tsutsumi, Suita-shi, both of Japan MatsushitaElectric Co., Ltd., Osaka, Japan [22] Filed: Dec. 10, 1969 [21]Appl.No.: 883,806

[73] Assignee:

FOREIGN PATENTS OR APPLICATIONS 1,005,293 12/1951 France ..336/l78Primary Examiner- Thomas J. Kozma Altome vStevens, Davis, Miller &Mosher [57] ABSTRACT Temperature increase becomes a problem with aflyback transformer of a television receiver since it handles a highvoltage. In order to cope with this, it has conventionally been theusual practice to make the core gap sufficiently great to provideallowance for the design. With such a construction, however, thetransformer becomes large in size, and the highvoltage stability thereofis deteriorated. In view of this, in accordance with the presentinvention, a temperature-sensitive ferrite is provided in the gap of thecore to prevent the slope of the B-H curve from becoming unduly smalland to stabilize the high voltage during normal operation. In case thetemperature is increased, the Curie point of this temperature-sensitiveferrite is utilized to improve the temperature stability of the flybacktransformer.

3 Claims, 9 Drawing Figures P ATENTEDHAY 91912 1 3,662,307

SHEET 1 BF 3 PRIOR ART 1 /6 PRIOR ART MAGNET/C FLUX 05/vs/rY BMAGNET/Z/IVG FOPCE H CORE GAP /00?) I NVENTORS.

TERUHIRO TSUKUDA TAKASHI TSUTSUMI TTORNEYS PATENTEDMAY 9 I972 SHEET 2 BF3 MdGA/EUZ/IVG' FGPCEH INVENTORS TERUHIRO 'TSUKUDA TAKASHI TSUTSUMI vTTORNEYS FLYBACK TRANSFORMER This invention relates to a flybacktransformer for television receivers which is adapted to provide a highvoltage that is stabilized with respect to temperature variations.

Generally, in a television receiver, the high acceleration voltageimparted to the picture tube is taken from the flyback transformer, buttemperature rise becomes a problem with the flyback transfonner sincethe latter handles high power. A large temperature rise can occurespecially if the AC input voltage becomes excessive or the horizontaloscillator frequency is deviated so as to be lower than 15.75 KC. Inorder to eliminate such a drawback, it has heretofore been the usualpractice to use a large core provided with a sufficient gap to allow forthe design.

Further, a color television receiver which consumes high power requiresa large-sized flyback transformer in the horizontal deflection outputportion thereof, wherein since high power is handled, it is essential tostabilize the high voltage so as to minimize variations in the pictureamplitude, beam convergence peculiar to shadow-mask type picture tubes,white balance, color purity and so forth. This high voltage is as highas about KV, and yet a capacity of 1 mA is required. In order tostabilize such a high voltage, there has been proposed a shunt regulatorsystem in which a voltage regulator tube is inserted in parallel withthe high voltage circuit and the feedback regulator system, a pulseamplitude induced in the secondary winding of the flyback transformerdue to variations of the high voltage appearing in the flybacktransformer being detected by a varistor or the like and then fed backto the horizontal output tube. However, these systems aredisadvantageous because they require a large number of circuit elements.

FIG. 1 shows the construction of a common flyback transformer, whereinnumeral 1 represents a ferrite core, 2 a gap, 3 a primary coil, and 4 ahigh voltage coil. By changing the gap 2 in accordance with thesaturation type B-H curve with a hysteresis of the ferrite core as shownin FIG. 2, there are obtained B-H curves representing various values ofa. From this, it will be seen that it is possible to obtain a curve witha lower value of p. by making the gap 2 greater.

In the conventional flyback transformer, the gap 2 is made so great thateven if a load is increased, the operating point may be located in thestraight portion of a 8-H curve. This is to prevent the temperature ofthe core from being increased due to an increase of the high voltagewhich results from the fact that when the transformer is operated in theneighborhood of the saturation point, is decreased by an increase of theload. With such an arrangement, however, the efficiency becomes low inthe normal operating temperature range. (The permeability of themagnetic circuit is low.) Furthermore, in order to achieve apredetermined inductance, a great number of turns is required whichmakes the transformer'bulky. Still furthermore, in case the horizontaloscillation frequency is deviated to be lower or the transformer is usedin a place where the ambient temperature is high, when there is provideda high AC input voltage, it is dangerous to use the transformer in theneighborhood of the saturation point. In such cases, therefore, thetransformer could not be used. Another disadvantage is that a furtherincrease of the gap deteriorates the high voltage stability as shown inFIG. 3.

The present invention is intended to eliminate the aforementioneddrawbacks.

It is an object of the present invention to provide a flybacktransformer having a temperature-sensitive ferrite inserted in a portionof the core, thereby eliminating a number of circuit elements which haveconventionally been required for stabilizing the high voltage.

Another object of the present invention is to provide a flybacktransformer which is stabilized with respect to temperature rise in thecase of anomalous operation of the television receiver.

Still another object of the present invention is to provide a flybacktransformer wherein a temperature-sensitive ferrite can be easily andrigidly mounted.

Other objects, features and advantages of the present invention willbecome obvious from the followingdescription taken in conjunction withthe accompanying drawings, in which:

FIG. 1 is a view showing a conventional flyback transformer;

FIG. 2 is a view showing B-I-I curves thereof;

FIG. 3 is a view showing the relationship between the gap of the coreand the internal resistance of the flyback transformer (the lower theinternal resistance, the higher the stability);

FIG. 4 is a side view showing the flyback transformer according to anembodiment of the present invention;

FIG. 5 is a view showing an approximate B-H curve of the flybacktransfonner of FIG. 4;

FIG. 6 is a view showing the 8-H curves of the flyback transfonner interms of the thickness and characteristics of the temperature-sensitiveferrite;

FIG. 7 is a view showing curves representing the effect of thetemperature-sensitive ferrite in terms of temperature variations; and

FIGS. 8 and 9 are views showing how to mount the temperature-sensitiveferrite in the flyback transformer embodying the present invention byway of example.

Referring to FIG. 4, numerals l to 4 represent a core, gap, primary coiland high voltage coil respectively, which are similar to those of theconventional flyback transformers. In accordance with the presentinvention, a temperature-sensitive ferrite member 5 utilizing the Curiepoint is inserted in the gap 2 instead of making the latter great as inthe prior art. This temperature-sensitive ferrite member 5 is made of aferrite which is ferromagnetic in an ambient temperature range but losesits magnetic property, so as to become paramagnetic when a predeterminedtemperature is reached. This material is provided in the portion of thegap 2, and the transformer is normally operated in the vicinity of thesaturation point as shown in FIG. 5, thereby improving the high voltagestability. This compensates for a decrease of the high voltage whichstems from the fact that p. is decreased due to an increase of the loadso that the anode current of the picture tube is increased. Thus, thehigh voltage stability is improved. Furthermore, in such an anomalousstate that the horizontal frequency is deviated for a high AC inputvoltage, if the ambient temperature is increased, then the temperatureof the ferrite is also increased so that it becomes paramagnetic. Thisis equivalent to an increase of the gap 2. Thus, it is possible toprevent the temperature of the flyback transformer from beingelevatedhThe use of a core provided with a stepped gap results in suchB-I-I characteristics as shown in FIG. 5. By providingatemperature-sensitive ferrite in this gap portion, a flybacktransformer can be obtained which provides high voltage stability for ahigh AC input voltage when the ambient temperature is high, therebymaking it possible to improve the performance of a television receiver.

FIG. 6 shows B-I-I curves in terms of an air gap andtemperature-sensitive magnetic material. As will be seen from thisFigure, the curve for the case where the gap is zero rapidly becomessaturated, so that p. is remarkably decreased when the operating pointis varied, so that L is decreased, resulting in abnormal operation ofthe flyback transformer. It will also be seen that for an increased gap,the permeability p. remains substantially unchanged even if theoperation point is changed, which makes no contribution to the highvoltage stability, and that when the temperature sensitive ferrite isinserted, there is a point where p. is suitably varied. Referring toFIG. 7, there are shown B-H curves for the cases where atemperature-sensitive ferrite is inserted and those for the cases whereno such ferrite is inserted, taking ambient temperature as a parameter.As will be seen from this Figure, in the absence of thetemperature-sensitive ferrite, as theambient temperature increases, thesaturation of the B-H curve becomes remarkably so that u is markedlydecreased with a result that L is changed. Consequently, the highvoltage generating circuit is brought into an anomalous operating state.

Description will now be made of the manner in which thetemperature-sensitive ferrite is mounted. As shown in FIG. 8, atemperaturesensitive ferrite 6 may be inserted in a recess 7 formed in acore 8. Alternatively, a temperature-sensitive ferrite 9 may be fittedin a groove 11 formed in a core 10. By making the thickness oftemperature-sensitive ferrite slightly smaller than the depth of thegroove or recess fonned in the core, it is possible to prevent theferrite from being damaged since no pressure is imparted thereto whenthe core is tightened. In this case, the temperature stability of theflyback transformer with respect to the anomalous operation is more orless deteriorated, but this constitutes no practical problem. An optimumhigh voltage stability point can be obtained by suitably selecting thedepth of the groove or recess formed in the ferrite core, the thicknessof the temperature-sensitive ferrite and its permeability value.

What is claimed is:

l. A flyback transformer having a ferrite core formed with an air gapand primary and secondary coils wound on said ferrite core for producinga high voltage in a television receiver, wherein the improvementcomprises a temperature-sensitive ferrite inserted in said air gap whichbecomes rapidly paramagnetic when the temperature of said ferrite isincreased beyond a predetermined value, said flyback transformer havinga relatively low magnetic reluctance at temperatures below saidpredetermined value and remaining unsaturated at temperatures above saidvalue thereby preventing excessive temperature rise.

2. A flyback transformer having a ferrite core formed with an air gapand primary and secondary coils wound on said ferrite core for producinga high voltage in a television receiver, wherein the improvementcomprises a temperature-sensitive ferrite disposed in engagement with arecess formed in said air gap with a configuration similar to saidtemperature-sensitive ferrite, said ferrite becoming rapidlyparamagnetic when the temperature of said ferrite is increased beyond apredetermined value, said flyback transformer having a relatively lowmagnetic reluctance at temperatures below said predetermined value andremaining unsaturated at temperatures above said value therebypreventing excessive temperature rise.

3. A flyback transformer as defined by claim 1 wherein said temperaturesensitive ferrite becomes rapidly paramagnetic when a predeterminedtemperature is reached.

mg l g UN'I'FEDiS'lA'JE S PATENT OFFICE CERTIFICATE OF CORRECTIONPatentNo; 3,662,307 Dated May 9. 19 72- j Teruhirb TSUKUDA et a1.

It iscertified that error appears in the above-ddenrified patent andthat said Letters Patent are hereby corrected as shown below:

I The correct name' of the Assignee should read I I Matsfishita ElectricIndustrial Co. Ltd

Signed and sealed this 3rd day 0f April 1973 (SEAL) 'Attest: v

EDWARD M. FLETCHER,JR. ROBERT GOT TSCHALK Attesting Officer Commissionerof Patents 33 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIOIIPatent No. 3,662,307 Dated, May 9, 19.72

lnvcmofls) Teruhir'o TSUKUDA et a1 It iscertified that error appears inthe above-identified patent and that said Letters Patent are herebycorrected as shown below:

The correct name' of the Assignee should read I Matsfishita ElectricIndustrial Co. Ltd

Signed and-sealed this 3rd day of April 19 73.

(SEAL) Attest:

EDWARD M.PLETCHER,JR. ROBERT GOT TSCHALK Attesting Officer Commissionerof Patents

1. A flyback transformer having a ferrite core formed with an air gapand primary and secondary coils wound on said ferrite core for producinga high voltage in a television receiver, wherein the improvementcomprises a temperature-sensitive ferrite inserted in said air gap whichbecomes rapidly paramagnetic when the temperature of said ferrite isincreased beyond a predetermined value, said flyback transformer havinga relatively low magnetic reluctance at temperatures below saidpredetermined value and remaining unsaturated at temperatures above saidvalue thereby preventing excessive temperature rise.
 2. A flybacktransformer having a ferrite core formed with an air gap and primary andsecondary coils wound on said ferrite core for producing a high voltagein a television receiver, wherein the improvement comprises atemperature-sensitive ferrite disposed in engagement with a recessformed in said air gap with a configuration similar to saidtemperature-sensitive ferrite, said ferrite becoming rapidlyparamagnetic when the temperature of said ferrite is increased beyond apredetermined value, said flybaCk transformer having a relatively lowmagnetic reluctance at temperatures below said predetermined value andremaining unsaturated at temperatures above said value therebypreventing excessive temperature rise.
 3. A flyback transformer asdefined by claim 1 wherein said temperature sensitive ferrite becomesrapidly paramagnetic when a predetermined temperature is reached.